Not a single staff member accused of abusing a child asylum seeker at Nauru has been charged for an offence and the centre's operator cannot guarantee the security of detainees, a Senate inquiry has heard.

It also emerged on Monday that on-the-job staff drug testing is not conducted at Nauru, despite allegations of guards trading marijuana for sexual favours from female detainees.

A picture drawn by a 10-year-old Nauru detainee.

Transfield Services, which runs the detention centre at Nauru, says there have been 67 child abuse allegations at the facility - 30 against staff and 37 against asylum seekers.

The allegations against staff relate to all service provides including Transfield, Wilson Security, the Salvation Army and Save The Children.

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Transfield's Kate Munnings said low use of a whistleblower hotline indicated the success of normal management structures.Credit:Alex Ellinghausen

As Fairfax Media reported on Friday, allegations against staff include that a security officer used "excessive force" to remove a minor from a bus, and that staff pushed or threw rocks at child asylum seekers, or touched them inappropriately.

Transfield Services Commercial & Strategy Manager Erin O'Sullivan said of the 67 allegations, 12 were referred to police. Of the allegations against staff, six staff members were dismissed, two were removed from the site and one was suspended. Ms O'Sullivan said she was "unaware of any charges being laid" over the alleged incidents.

A Transfield director, Angela Williams, could also not guarantee that the staff members had been permanently dismissed from the centre, saying they may have been reassigned to a different section or stood down pending investigation.

Transfield Services said the definition of child abuse was broad, and included children fighting and inappropriate discipline within families, as well as alleged abuse by staff.

Senator Kim CarrCredit:Alex Ellinghausen

The company is being paid $1.2 billion over 20 months to run detention facilities at Nauru and Manus Island as part of the controversial offshore processing regime instigated by the former Labor government.

The contract expires at the end of October. Labor senator Kim Carr asked how the firm reconciled the serious allegations of abuse at Nauru with its commitment to upholding human rights at the facility.

The independent Moss review into sexual abuse at the Nauru detention centre found evidence of rape, sexual assault of minors and guards trading marijuana for sexual favours from female detainees

Transfield Services told the hearing in Canberra that while random alcohol testing of staff took place daily, on-the-job drug testing "can't be done" because of limited pathology services on the island.

Transfield's operations chief executive Kate Munnings said "behavioural indicators" and other measures were used to manage the risk of drug use among staff.

Ms Munnings said it takes its human right obligations seriously and staff "hold paramount" the safety of asylum seekers, and the company acted "decisively and appropriately" when allegations were made.

She refused to guarantee the security of all detainees when prompted, saying the company worked with all stakeholders to ensure care and welfare was provided.

Greens senator Sarah Hanson-Young sought detail on 402 instances of Transfield Services employees who had been dismissed at Nauru and Manus Island.

Ms Munnings said this included staff who abandoned their role by not turning up for work.

She was unable to say how many were dismissed for being intoxicated, despite Transfield having a strict drug and alcohol policy.

Senator Hanson-Young raised concerns over a child who was allegedly abused by a staff member at Nauru in 2013, but remained in the centre. She said after the alleged offender was fired, the child suffered further abuse and humiliation as "retribution" from other staff.

Transfield Services said the Immigration Department was responsible for the decision to leave the child in detention.

The inquiry heard facilities at Nauru were initially "rudimentary", resulting in electricity outages and water shortages.

Transfield official Daron White, who manages logistics and facilities at the centre, said the provision of adequate water had been "challenging".

In the early days of the detention centre, 450,000 litres of water were available each day for asylum seekers and workers, Mr White said. This is despite about 1200 asylum seekers using up to 300 litres of water per person per day – or 360,000 litres - on top of the 1500 workers on the island who required water supplies.

This led to water rationing, two-minute shower rules and workers being instructed to skip showers to leave sufficient supplies for asylum seekers.

There have been allegations that a local officer gave additional shower time if an asylum seeker exposed themselves.

Earlier information supplied to the inquiry by Transfield Services revealed there had not been a single call to the whistleblower hotline set up for staff to make complains or report abuse.

On Monday Ms Munnings said there had since been two calls to the hotline.

Senator Hanson-Young questioned how well the hotline was promoted to staff, and suggested it was not operating effectively.

Transfield Services told the inquiry the hotline was advertised to staff, who were made aware of it during job inductions.

Staff could also report abuse to their managers, security or through other means, Ms Williams said.

Senator Carr suggested low use of the hotline reflected a lack of confidence in protections for whistleblowers.

Ms Munnings said it showed the "quality and capability of management" that staff did not feel the need to raise matters through the hotline.